The name is derivative form of the given name Genevieve - "white crow/phantom".
Guinevere was the legendary Queen consort of king Arthur. In tales and folklore, she was said to have had a love affair with Arthur's chief knight Sir Lancelot. This story first appears in Chrétien de Troyes' Lancelot, the Knight of the Cart, and reappears as a common motif in numerous cyclical Arthurian literature, starting with the Lancelot-Grail Cycle of the early 13th century and carrying through the Post-Vulgate Cycle and Thomas Malory's Le Morte d'Arthur. Guinevere and Lancelot's betrayal of Arthur was often considered as having led to the downfall of the kingdom.